import java.util.ArrayList;
import java.util.List;

public class CountSmaller {
    int[] ret;
    int[] index;   //标记原始下标
    int[] tmpIndex;
    int[] tmpNums;
    public List<Integer> code(int[] nums) {
        int n = nums.length;
        ret = new int[n];
        index = new int[n];
        tmpIndex = new int[n];
        tmpNums = new int[n];

        //初始化index数组
        for (int i = 0; i < n; i++){
            index[i] = i;
        }

        mergeSort(nums, 0, n - 1);

        List<Integer> l = new ArrayList<>();
        for (int x : ret){
            l.add(x);
        }

        return l;
    }

    public void mergeSort(int[] nums, int left, int right){
        if (left >= right){
            return;
        }

        int mid = (left + right) / 2;
        mergeSort(nums, left ,mid);
        mergeSort(nums, mid + 1, right);

        int cur1 = left, cur2 = mid + 1, i = 0;
        while (cur1 <= mid && cur2 <= right){
            if (nums[cur1] <= nums[cur2]){
                tmpNums[i] = nums[cur2];
                tmpIndex[i++] = index[cur2++];
            }else{
                ret[index[cur1]] += right - cur2 + 1;
                tmpNums[i] = nums[cur1];
                tmpIndex[i++] = index[cur1++];
            }
        }

        while (cur1 <= mid){
            tmpNums[i] = nums[cur1];
            tmpIndex[i++] = index[cur1++];
        }

        while (cur2 <= right){
            tmpNums[i] = nums[cur2];
            tmpIndex[i++] = index[cur2++];
        }

        for (int j = left; j <= right; j++){
            nums[j] = tmpNums[j - left];
            index[j] = tmpIndex[j - left];
        }
    }
}
